The present invention relates to an image-taking apparatus which achieves improved accuracy in taking an image through image shake correction.
In recent years, automation of all the operations in taking images such as exposure determination and focusing has reduced the probability of failing to take good images even when a camera user has only a little knowledge about the camera. In addition, an image shake correction function allows a user to take better images. An image stabilization system for preventing image shake will be described below.
A camera typically shakes at a wavelength between 1 Hz and 10 Hz in taking images. A basic idea for suppressing the shake at the time of exposure to take an image without blurring is to detect the shake of the camera from image shake and displace a correction lens in a plane orthogonal to an optical axis in response to the detection result. In other words, to take an image without blurring even when the camera shakes, it is necessary to accurately detect the shake of the camera in the first place, and to correct the change of the optical axis due to the image shake in the second place.
The image shake correction described above can be performed in principle such that a laser gyro or the like detects the acceleration, angular acceleration, angular velocity, angular displacement and the like, and a shake detector is provided for the camera to perform calculations of the detection result as appropriate.
A correction optical apparatus is driven to move the optical axis for image-taking based on the information about the camera shake detection output from the shake detector. Image shake correction is achieved in this manner.
Another method has been proposed in which image-taking is repeated a plurality of number of times with an exposure time set to involve no image shake, and the images provided through these image-taking operations are combined while their displacements are corrected, thereby providing the taken image (the combined image) with a long exposure time (Japanese Patent No. 3110797).
When the image-taking magnification is smaller than 0.1, any shake can generally be corrected by optical image shake correction (optical image stabilization) through angular shake correction. However, when the image-taking magnification is larger than 0.1, shift shake has a larger influence. If the image-taking magnification is even larger, shake in a focus direction has a lager influence. Thus, the effect of image shake correction cannot be provided sufficiently when the optical image stabilization is employed in a device with a high image-taking magnification such as a macro lens.
On the other hand, when moving images are taken by a video camera, electronic image stabilization has been proposed in which motion vectors in an image are detected by an image-pickup device and the read position in the image is changed to match the motion vectors to provide moving images without shake.
In the electronic image stabilization, however, the motion vectors are detected in the video camera by taking a plurality of images out in one second and comparing the respective taken images. When a digital camera is used to take a still image with only one exposure for a taken subject, it is not possible to detect motion vectors by comparing images in frames. As a result, the image stabilization system for the video camera cannot be applied to the digital camera.
Japanese Patent No. 3110797 has disclosed the electronic image stabilization technique in which image-taking is repeated a plurality of number of times and the images provided through these image-taking operations are combined while their displacements are corrected, thus providing a taken image. However, the image-taking repeated a plurality of number of times causes a long image-taking time, and the sufficient effect of correction cannot be provided due to a subject movement or the like.
In addition, in the technique disclosed in Japanese Patent No. 3110797, a user should determine whether or not he/she needs to take action for image stabilization. However, it is difficult for the user to determine whether or not the action for image stabilization is required at the site of image-taking, which makes the technique less convenient for the user.